Centrifuges are commonly used in medical and biological industries for separating and purifying materials of differing densities, such as viruses, bacteria, cells and proteins. A centrifuge includes a rotor and a container to support a sample undergoing centrifugation. The rotor is designed to hold the sample container while it spins at 3,000 to 120,000 revolutions per minute.
Two requirements for the centrifuge rotor and sample container have historically been in conflict: strength and weight. That is, the centrifuge rotor and sample container must have the requisite strength to resist forces associated with centrifugation and should be manufactured from the lightest weight materials available. At first, centrifuge rotors and sample containers were constructed from metal alloys, such as steel, which provided acceptable strength. However, the weight associated with these metals subjected the load bearing sections to forces that limited their operational life. In addition, the centrifuge time of a sample in the heavy rotors were protracted due to a the limited speed of the rotor, as well as the protracted acceleration and deceleration times which are a function of the rotor's moment of inertia.
Early attempts to overcome the aforementioned drawbacks, resulted in manufacturing rotors and sample containers from alternative metals, such as titanium and aluminum. However, these materials are proving too heavy to obtain the desirable weights and speeds for modern medical practices and biological research. In addition, these materials are costly to machine, resulting in a sharp increase in the costs of a centrifuge system.
Fiber reinforced centrifuge rotors and sample containers have overcome many of the drawbacks of past centrifuge components. These rotors are stronger and lighter than metal rotors and provide a much smaller moment of inertia, as well as higher maximum speeds. U.S. Pat. No. 5,362,301 to Malekmadani et al. discloses a fixed angle all composite centrifuge rotor. The rotor includes a plurality of slots equally spaced about the circumference of the rotor, with reinforcement cups placed therein. The cups are formed of a plurality of helically wound fibers which are dipped in an epoxy matrix.
U.S. Pat. No. 5,382,219 to Malekmadani discloses a fixed angle all composite centrifuge rotor including a plurality of tube holders equally spaced about the circumference of the rotor. Each of the tube holders a formed from a plurality of helically and circumferentially wound layers of fiber material dipped in an epoxy matrix.
The all fiber reinforced holders are incompatible for providing close tolerance fittings which often requires machining, or grinding, of the fiber reinforced surface. This degrades the fiber reinforced material and leads to a reduced operational life and/or complete failure of the holder during centrifugation. Often when close tolerance fittings are required, a separate container is placed in the holder, such as a plastic or metal centrifuge tube or bottle. This increases the weight and creates problems associated with earlier centrifuge components. Recent attempts have been made to address this problem. In PCT application No. PCT/US92/09104 to Beckman Instruments, Inc., a hybrid centrifuge container is disclosed which provides a durable light weight sample holder capable of being machined to close tolerances. The container includes a fiber reinforced base having an open end and a closed end, with a metal sleeve attached to the open end.
An object of the present invention is to provide a hybrid centrifuge container capable of being machined to close tolerances and that is lighter than the containers of the prior art and has a substantially longer operational life.